Folks,
Thanks for the advice and pointers. I managed to download Malwarebytes onto another computer, copy it, load and run it on mine - it found and removed all sorts of stuff, including the main culprit, which was Fakespypro. However, that returned after restarting, and did the same again after another run through, so it had obviously embedded itself thoroughly.
On the basis that I had already backed up all my working files before it appeared, had loaded relatively few applications, and my expertise had run out, I took a deep breath and ran the Dell factory restore option, which reformats the hard drive and reinstalls the system to the original spec.
Thankfully, this has worked and got rid of the problem completely, so I'm back up on line and firing on all cylinders now, with just a few settings to change and a slack handful of stuff to load back up. The experience certainly reinforced the value of backing up personal files regularly.....
Thanks again,
MG Mark